Titanium σ-acetylides as building blocks for heterobimetallic transition metal complexes: synthesis and redox behaviour of π-conjugated organometallic systems

Abstract

A series of related Ti σ-acetylides of the type {Ti}CCR ({Ti}=(η 5-C 5H 5) 2Ti(CH 2SiMe 3); 2: R=SiMe 3; 3: R=C 6H 3(CH 2NMe 2) 2-3,5; 4: R=C 6H 2I-4-(CH 2NMe 2) 2-3,5; 5: R=C 6H 4CN-4; 6: R=C 5H 4N-4; 7: R=Fc, Fc=(η 5-C 5H 4)Fe(η 5-C 5H 5); 8: R=C 6H 4(CC{Ti})-4) have been prepared by reacting the corresponding lithium acetylides with {Ti}Cl ( 1). The X-ray crystal structure determination of {Ti}CCSiMe 3 ( 2) is reported. This compound exhibits a one-dimensional (1D) arrangement with respect to the Ti–CC unit. The reaction of 2 with [CuCl] n afforded 1 and [CuCCSiMe 3] n ( 10) and is proposed to occur via prior formation of the dimeric intermediate [(η 2-{Ti}CCSiMe 3) 2Cu 2Cl 2]. The chemical oxidation of {Ti}CCFc, 7, with Ag[BF 4] yielded HCCFc and an undefined Ti species. Treatment of 5 or 6 with {Ru}NN{Ru} ({Ru}= mer, trans-[RuCl 2(NN′N)]; NN′N=η 3-C 5H 3N(CH 2NMe 2) 2-2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}CCC 5H 4N-4]{Ru} ( 16). In contrast, 5 and 6 react with cationic Pt compounds of the type [{Pt}·L][X] ({Pt}=[Pt(C 6H 3{CH 2NMe 2} 2-2,6] +; L=H 2O, MeCN; X=BF 4, OTf) to give product mixtures rather than defined compounds. Electrochemical studies on some of the bimetallic compounds show that the Ti(III)/Ti(IV) redox potential appears to be reversible and is shifted to a more negative value upon substitution of the Cl ligand in 1 by CCR (compounds 2– 8). Whereas the nature of R in {Ti}CCR has an influence on the Ti(III)/Ti(IV) redox potential, the attachment of a second metal onto the π-conjugated system has only negligible effect on the electrochemical properties of the Ti centre.